This core resource provides crystallographic and molecular modeling tools to assist in the design and analysis of candidate hemoglobin-based oxygen carriers. Core 1 will specifically support two research projects; Project 1: Recombinant hemoglobins as artificial oxygen carriers and Project 2: Intramolecularly cross-linked hemoglobins. Each of these projects requires detailed molecular modeling studies of proposed oxygen carriers to assess the potential for obtaining molecules with the appropriate oxygen affinity and properties. The three-dimensional structures of the oxy-, de-oxy-, and liganded forms of those molecules selected for further study will assess how the structure differs from human hemoglobin and the predicted structure. This information will assist in improving the design (or properties) of these proteins.